Optical setup: Ha lamp => diffuser => etalon => Nikon Z6 with 85 mmS f/1.8 lens
Interference fringe pattern
Lunt LS40FHa - Interference fringe pattern - Nikon Z6 - 85 mm S f/1.8 Nikkor lens at f/2.2 (i.e. 37.4 mm aperture) - 12-bit RAW file - 0.5 s - 100 ISO - 22 November 2024
Comments:
- The interference patern is quite uniform with a nice Lorentzian profile for the rings.
- The mesurements from the different rings are very consistent.
- There is a very slight improvement in the FWHM when the aperture is stopped down to 15 mm.
- The mesurements from the different rings are very consistent.
- There is a very slight improvement in the FWHM when the aperture is stopped down to 15 mm.
Spectro measurement in a collimated beam
Optical setup: Sun => etalon => Solex with 7 microns x 6 mm slit, fc = f i =200 mm, 2400 l/mm grating, ASI 290, 0.0471 A/pixel dispersion
Top image : spectrum transmitted by the etalon.
Bottom image : solar spectrum.
The transmission profile (= transmitted spectrum/solar spectrum) consists in textbook Lorentzian curves (curve fitting with Fityk).
FSR increases with the order of interference (as expected). Fringe #4 is on Ha:
The values for Ha (fringe #4) are :
FWHM = 0.57 A and FSR = 11.8 A.
Spectro measurement in a f/35 telecentric beam
Optical setup: Sun => C8 EdgeHD => f/35 telecentric => etalon => Solex with 7 microns x 6 mm slit, fc = f i =200 mm, 2400 l/mm grating, ASI 290, 0.0471 A/pixel dispersion
Curve-fitting done on etalon transmission = transmitted spectrum/solar spectrum :
Test of the etalon in Ha collimated beam
Optical setup: Ha lamp => 3 mm aperture stop => 55 mm f/8 collimating fluo doublet => etalon in collimated light (equivalent to f/146 ratio) => Nikon Z6 with 105 mm f/2.8 S macro lens
Comments:
This test is quite demanding and shows any on uniformity of the etalon. The etalon under test is clearly very uniform. Traces of the manufacturing process are visible.